A hundred years ago, children in their minds multiplied many-digit numbers. Simple ways to replace long multiplication
There is such a picture of Nikolai Bogdanov-Belsky (1868-1945) “Oral account. In the folk school of S.A. Rachinsky "in the Tretyakov Gallery:
It depicts a scene from the 19th or early 20th century (judging by the time when the artist lived), where the teacher wrote an example on the blackboard and the children solve it, they perform complex arithmetic operations in their minds. Here's a close-up example:
It’s not something that’s in your head, you cannot solve quickly on a calculator without writing down intermediate actions on paper. Although, it can be solved quite simply if you know the degrees of the main numbers. The solution is on the third slide.
It turns out that there are many ways when, at first glance, complex arithmetic problems can be solved very simply. Although, at school we were offered only one way - this is addition-subtraction and multiplication-division by a column. But such methods, including quick graphical solutions, were not mentioned:
Easy ways to multiply two-digit numbers. The action algorithm is simple and easy to remember.
This is also a simple rule: you need to divide a factor or quotient by two numbers (or more) and perform calculations in several steps. The simplest is when the multiplier can be split by 10 and another number. Add zero to the multiplicand and multiply by the second number.
Mathematical pyramid. Harmony in numbers.
A video with similar calculation techniques:
In some cases it is necessary to record intermediate results. But this is easier than multiplying into a column. These are far from the only ways. There are many of them: simple and more complex.
Ways to convert degrees Fahrenheit and back. Sometimes the American temperature measurement system is found on some devices. The values can be easily translated mentally into the usual degrees of Celsius.
Mathematical techniques must be constantly kept in mind and used regularly. Otherwise, everything is forgotten. Like school theorems and physics formulas. In the modern world, we are less and less faced with cases where such skills are needed. But they are the basis in a person's cognitive abilities to think, apply logic. They even stopped reading books - replaced it with scrolling through the news feed and subscribing to content with photos.
Mind training should be in a person throughout his life. By losing cognitive skills, people lose the ability to analyze and compare facts. And it becomes easy to manipulate us.
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